Why do the permissions of a symbolic link default to all-permissive?
Which platform are you working on?If you are on linux, then symlink permissions are not used at all, so whatever their value nobody cares. That could be different on BSD, OSX, or other flavors.
This question could be better answered on unix sub forum I guess.
I discovered that the default permissions for a directory are 777
Hmm, I don't really know where you get that from. Default permissions for file and directories (still on linux) just depend on the umask of the process. See man umask.